wireframe,surface or solid and finite element analysis.

Discussion in 'Pro/Engineer & Creo Elements/Pro' started by yogesh, Jul 12, 2004.

  1. yogesh

    yogesh Guest

    following is the text from sdrc ideas tutorial

    "I-DEAS uses a solid representation of part geometry.Because it's a
    complete representation, solid geometry supports any type of design
    and analysis application that requires geometry information.
    For example, it gives finite element simulation "

    Now my question is , suppose I supply a similar representation of a
    particular solid in pure wireframe format( say using autocad),can I do
    FEM analysis on it.

    My friens who is working on Hypermesh told me that hypermesh has very
    limited modeling capabilities but whenever need arises he can create a
    wireframe model of a solid and does fem analysis on it.
    He also told me that many times the CAD models are not complete and
    has some incomplete features.So they repair it in hypermesh using
    line,spline commands and then it is used for FEM.

    He said to me that geometry is required only for reference and meshing
    is a totally different issue.

    what is correct? I am totally confused. (as usual :).

    regards,
    Yogesh Joshi
     
    yogesh, Jul 12, 2004
    #1
  2. yogesh

    Jeff Howard Guest

    -----------------------------------------

    Finite element analysis always requires the creation of analysis elements
    (planar mesh, solid mesh, bar, rod, etc.). Nurbs, bezier, etc. surfaces
    used for most present day "solid" reps are of no use to the solver, but most
    pre-processors can reference them for mesh generation so you are money ahead
    sending a solid (or surface) vs. wireframe rep to it.

    " ... he can create a wireframe model of a solid ..." The wireframe is just
    a reference for element / mesh creation.

    "... many times the CAD models ar not complete..." If the model is supposed
    to be a solid rep any "incompleteness" is due to something getting lost in
    translation. (Actually, most solid models contain too much detail for FEA
    purposes.)

    Basically, the I-DEAS statement is marketing psycho-babble. All the
    attributes given to the "solid" can also be given to any set of surfaces
    that define a volume; e.g. a closed surface or quilt. Once a volume is
    defined, all that's necessary to have a "solid" is a database entitiy for
    mass.
     
    Jeff Howard, Jul 12, 2004
    #2
  3. yogesh

    yogesh Guest

    Thanks Jeff!
    but still I have some doubts..
    Suppose I draw a cube using only 3D lines and I draw the same cube
    using solid modeling operations(extrusion).
    How will fem solver treat them..?
    in similar or in different manner.?


    regards,
    Yogesh Joshi
     
    yogesh, Jul 12, 2004
    #3
  4. yogesh

    Jeff Howard Guest

    The solver won't deal with either one. It can't see the wires or surfaces.
    In either case the user will have to mesh the objects using whatever
    functions are available in the pre-processor. The meshing operation is
    quite similar to other surface modeling techniques (exactly like creating an
    old Acad polyface mesh, if you are familiar with that) for shell / plate
    models. Where surface data is present most pre-processors can auto mesh the
    surfaces for a shell / plate model or fill the volume with a 3D mesh for a
    solid solution, with at least some degree of success. I don't have the
    foggiest how the solver internal math works, but it requires a matrix of
    "nodes" to do the computations. These nodes are the corner vertex (at
    least) definitions of "elements". Neither wireframe models nor surface /
    solid models created by CAD systems have any representation of this node
    matrix. (The exception being the previously mentioned polyface mesh models.
    These will translate directly to FEA mesh; all that the user has to do is
    merge coinicident nodes, define material and properties, etc.)
     
    Jeff Howard, Jul 12, 2004
    #4
  5. yogesh

    meld_b Guest

    Sure, your friend is technically right, you can do FEA with just
    wireframe. But once you need to do a fairly complex part, using a solid
    model and a decent modern mesher (not sure SDRC qualifies :cool: will be
    MUCH faster. Of course that's not to say you shouldn't learn what FEA is
    all about and how far the tools will take you. Vince Adams' book on FEA
    is a very good thing to read.

    I think there was a day when modelers automatically redrew everything,
    mainly because meshers used to be pretty poor, as well as some CAD
    systems. Now days, if you don't have a setup that can mesh a fairly
    complex molded part, solve it, and get the right answer (converged)
    rather quickly, then you need to be out looking at a new system.

    Might be fun to compare FEA systems too. There ARE some differences...

    -meld
     
    meld_b, Jul 13, 2004
    #5
Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.